Henipaviruses show increasing impact as causes of central nervous system illness in the human community. We propose to apply our understanding of paramyxovirus entry to the development of new strategies for inhibiting infection that will apply to newly emerging paramyxoviruses. The first step in paramyxovirus infection is the binding of the receptor-binding protein (G for Hendra and Nipah viruses;HeV/NiV) to receptor on the cell's surface (EFNB2 for HeV/NiV). Receptor engagement activates the viral fusion proteins (F) to fusion-ready conformation, and F then inserts into the target cell membrane, fusing the viral envelope with the cell's membrane and allowing viral entry. In a novel therapeutic approach, we will identify compounds that induce F to trigger prematurely, inactivating the viruses before they can enter the target cells. 1. Proof of concept for new antiviral platform: Paramyxovirus receptor mimics induce premature triggering of F distant from the target cell. This aim will test the hypothesis that if G-receptor interaction can be mimicked before an infectious viral particle binds to the cell surface, F can be induced to be triggered prematurely and be inactivated. We will assess whether soluble receptor-mimicking molecules inhibit multicycle replication in relevant tissue models for human vascular endothelium and for human CMS parenchymal cells. Support of this aim includes evidence for "premature triggering" of F for a related paramyxovirus, and that receptor-coated microparticles irreversibly inactivate pseudotyped henipaviral particles. 2. High-throughput screening (HTS) of a chemical library for compounds that stimulate untimely activation of viral fusion mechanisms. We have developed a novel assay for multicycle replication of HeV/NiV pseudotypes, and screening assays for neutralizing antibodies and antiviral compounds (now adapted to HTS). To identify compounds that may stimulate untimely activation of viral fusion mechanisms we will assess compounds specifically for premature triggering activity. Effective compounds will then be tested vs. live virus. Structural modeling, based on new crystal structures if needed, in collaboration with W, Welsh (Snowdon, Inc.) will provide another approach to identify potential inhibitory compounds. The results will lead to: validation of a new antiviral strategy. If efficient receptor-mimics can trigger and thus inactivate F after budding and release, released virus could be rendered noninfectious and viral spread halted. Strategies devised based upon G-F interaction will likely apply to new paramyxoviruses and other pathogens that trigger the key activities of cell entry only at a specific time and place to initiate infection.